Sole stiffness affects stance time
By Erin Boutwell
A recent study published in the winter issue of Pediatric Physical Therapy found that children just learning to walk may have altered gait characteristics when wearing flexible shoes.
Whether novice walkers should wear flexible or stiff shoes is not a new question, said Melanie Buckland, DPT, at the Hospital for Special Surgery in New York City and study author, but it is a frequent question fielded by pediatricians and physical therapists.
Previous studies have associated stiff shoes with the delayed development of arches in early walkers, and arch development is often the primary focus of the flexible versus stiff shoe debate. However, Buckland and her coauthors contend that shoe flexibility may also have an important influence on children’s functional activities, especially walking and balance.
Buckland’s study investigated the gait and stability of 25 early walkers, children aged 9 to 24 months who had been walking for less than five months. Four shoes with different torsional flexibilities (from
most flexible to least: UltraFlex, MedFlex, LowFlex, and Stiff) and a barefoot condition were compared during level walking.
While walking speed and step length were not affected by shoe flexibility, stance time was significantly lower for the most flexible shoe (UltraFlex) than the LowFlex shoe. Additionally, the barefoot condition was associated with a significantly shorter stance time than any shod condition.
Buckland attributed the shorter stance time in the UltraFlex condition to improved sensory feedback, saying, “We believe they were able to feel the ground better with the more flexible shoe…and they were able to accommodate and go ahead and take another step.”
Elaine Owen, MSc, superintendent physiotherapist at the Child Development Center in Bangor, North Wales, UK, proposed an alternative explanation: Reduced stance time could be a result of biomechanical effects of the footwear.
“The stiffer the material…the longer it will take for the MTPJs [metatarsophalangeal joints] to extend to the amount they need to by end of stance,” Owen explained.
In addition to gait, Buckland and her coinvestigators designed an obstacle course to assess the stability of these early walkers by counting the number of falls and stumbles. No significant differences were found among the various shoes, nor did children perform better when barefoot than when shod.
That stability was unaffected by shoe flexibility is a surprising result, as work published in 2013 by researchers at the Hospital for Special Surgery in the Journal of the American Podiatric Medical Association demonstrated that increasingly flexible shoes were associated with greater plantar loading in the same group of early walkers.
The authors of that paper, Buckland among them, identified plantar loading as a mechanical feedback mechanism that could improve these early walkers’ proprioception. The authors also anticipated that stability might be improved in a more flexible shoe if the child was able to take advantage of the intrinsic structures of the foot.
“The foot is made up of many small bones and joints for mobility,” Buckland explained, “so the foot needs to be very mobile, flexible, able to accommodate to the ground for balance.”
In the current study, stability—as evaluated through stumbles and falls—was not related to shoe flexibility. However, step width was larger in the UltraFlex shoe compared with the MidFlex and LowFlex shoes. According to the study authors, this finding is a possible indication of reduced gait stability with the most flexible shoe.
Increased step width is often associated with a reduction in stability, but other explanations are possible. Coronal plane curvature in the shoes themselves may have contributed to an unstable base in the mediolateral direction, Owen suggested.
Three of the four tested shoes were made by the same manufacturer, while the Stiff shoe was produced by a different company. Buckland acknowledged that factors such as heel height, position of the toe break, and insole materials—none of which were controlled in the current study—could influence how children walk in these shoes.
Owen asserted that the shoe profile is a primary consideration when considering gait biomechanics.
“You can walk very well in a stiff shoe as long as you have the right profile on the shoe,” she said. “A lot of stiff shoes actually have a rounded profile.”
Nonetheless, Owen affirmed that flexibility is a significant factor in shoe design.
“I feel that the footwear should be very flexible, the most important reason being to use the windlass mechanism [critical in arch development]…if stiffness is introduced, this does not occur,” she said.
Similarly, Buckland emphasized the importance of continuing to explore the effects of shoe flexibility.
“With further research, we can really help these kids promote their development and their gross motor skills,” she said.
Erin Boutwell is a freelance writer based in Chicago, IL.
Buckland MA, Slevin CM, Hafer JF, et al. The effect of torsional shoe flexibility on gait and stability in children learning to walk. Pediatr Phys Ther 2014;26(4): 411-417.
Hillstrom HJ, Buckland MA, Slevin CM, et al. Effect of shoe flexibility on plantar loading in children learning to walk. J Am Podiatr Med Assoc 2013; 103(4):297-305.